In 2019, the U.S. Department of Defense began investing in the military use of balloons under its COLD STAR (Covert Long Dwell Stratospheric Architecture) progr

In 2019, the U.S. Department of Defense began investing in the military use of balloons under its COLD STAR (Covert Long Dwell Stratospheric Architecture) program.[27] The Pentagon began incorporating high-altitude balloons into the military kill chain with a focus on hypersonic weapons, in line with the Space Development Agency program for commercial satellite constellations.[28] Balloons could be preferred as a platform for their low cost, lower altitude, and less predictable trajectories compared with satellites." https://wikipedia.org/wiki/2023_Chinese_balloon_incident#History_of_spy_balloons https://wikipedia.org/wiki/2023_Chinese_balloon_incident#His...